The present invention generally relates to multi-function testers for performing electrical tests, and more specifically to such a multi-function tester which includes removable and interchangeable cartridges or modules which contain electrical elements required to perform electrical tests, and which includes an indexing or a switching arrangement which is simple in construction and facilitates the selection of the tester function.
Numerous multi-position probes or testing devices for testing electrical circuits are known. Such probes are commonly used for servicing and repairing electronic equipment and involve the determination of electrical characteristics of electrical circuits. Common tests which are performed with such simple test instruments include the measurement of a voltage or resistance between two probes of the device or the current flowing through the two probes. The devices under discussion are frequently called multi-function devices or testers because they can perform two or more of the aforementioned tests by selecting the position of a switch which is provided on the probe or test unit. However, the multi-function testers known in the art have several important disadvantages. Firstly, some of these devices are complex in construction and, therefore, expensive to manufacture. Additionally, the electrical circuitry within the probe units is frequently permanently attached to the case or housing of the tester and may be inaccessible for purposes of repair or replacement.
Another disadvantage of the prior art devices is that they are limited to the two or more tests for which they are designed and their testing functions cannot be expanded once the test unit is assembled. An additional disadvantage of many prior art units is the difficulty or inconvenience with which the different functions are selected or changed during use of the device.
The above-described prior art devices are exemplified in U.S. Pat. Nos. 2,540,402; 3,196,217 and 3,315,163. In U.S. Pat. No. 2,540,402, for an electrical testing probe, there is shown a test unit which includes a rotatably mounted end knob. However, this knob only has the function of closing or opening a light circuit or energizing a bulb which lights the main or primary probe of the unit. The selection of the desired function in the patent under discussion is achieved by a series of jacks into which one of the probes is selectively inserted.
A multiple-position switch is disclosed in U.S. Pat. No. 3,196,217. This patent discloses a front or nose section which is rotatably mounted with respect to a rear barrel, with the relative position of the nose being selected by a resilient detent means. However, as suggested above, the components are mounted or connected directly to the rear barrel and, for this reason, are not conveniently accessible for repair or replacement. The meter probe with slidable circuit changing contact point of U.S. Pat. No. 3,315,163 has similar disadvantages. However, here the switch selector is a sliding member which has spring contacts for making successive engagements with various electrical contacts within the probe case. However, the last mentioned patent has a relatively complex construction and therefore is expensive to manufacture. None of the above-mentioned patents disclosed a multi-function tester which has a module or cartridge which contains electrical circuitry associated with the various tests to be performed, which cartridge or module is removably insertable into the tester case and may be conveniently and quickly changed to replace a defective cartridge or to change the functions or tests which are to be performed.